1. Field of the Invention
The present invention relates to a method and apparatus for providing scanning with a light transmitter (such as an optical fiber), of particular but by no means exclusive application in microscopy, endoscopy (including endomicroscopy), and confocal microscopy and endoscopy.
2. Description of the Related Art
Some existing microscopes and endoscopes employ one or more optical fiber for light delivery to a sample and light collection from the sample. To image the sample, the delivered light is scanned across the sample; by scanning the exit tip of the fiber, this can been done by scanning the light after its emission by the fiber, or by providing multiple return fibers and collecting light sequentially from each.
The scanning of the fiber can be effected by attaching the exit tip of the fiber to a mechanical actuator, such as a vibrating tine of a tuning fork. Alternatively, one existing approach employs an actuator located at the base of a fiber, to impart a scanning motion to the fiber and hence its tip.
For example, four background art scanning mechanisms 10, 12, 14, 16 for use in small diameter endoscopes are shown in FIGS. 1A to 1D respectively. Scanning mechanisms 10 and 12 of FIGS. 1A and 1B each include an asymmetric fork 18 of ferromagnetic material to carry an optical fiber (not shown). A first (scanning) tine of fork 18 is axially located and a fixed X drive coil 20 surrounds both scanning tine and the second (balancing) tine. A Y scan is obtained by a see-saw action whereby the fork 18 rocks inside the X coil 20. The driving force for the Y scan is obtained with a permanent magnet 22 and an electromagnet 24 that carries a Y drive current. In scanning mechanism 12 of FIG. 1B, the magnetic circuit is folded to reduce overall length, and the Y coil 24 is hollow.
Synchronisation in both scanning mechanisms 10 and 12 is obtained with a piezo sensor mounted at the base of fork 18, which is used to drive the fork at resonance through an amplifier. The X scan in both mechanisms is sinusoidal, and usually the central half of the mechanical scan is used for imaging. The outer scan region, where the fiber tip slows down and reverses, is discarded.
Scanning mechanism 14 of FIG. 1C is the base excited cantilever using a tube piezo driver. This layout is seen in scanning microscopes, bar-code scanners, and a spiral scanning endoscope developed at the University of Washington. Such systems appear, however, to suffer from problems in the control of scan distortion.
Referring to FIG. 1D, scanning mechanism 16—disclosed in WO 04/40267—includes a slotted magnet 26 attached to a fiber 28 near the base 30 of the fiber, such that the fiber acts as a vibrating cantilever. The magnet 26 is activated and controlled by four electromagnets or coils 32 that surround the magnet.
Examples of some of these scanning systems are disclosed in U.S. Pat. No. 6,294,775, U.S. Pat. No. 6,975,898 and U.S. Pat. No. 6,845,190.